Metallic alloys are widely used in restorative dentistry for permanent replacement of lost tooth and bone structure. There has been growing concern within the dental profession that alloys developed as alternatives to high-cost noble metals may corrode more, causing increased problems regarding loss of substance and weakening of the metal and/or toxic or allergic reaction to the corrosion products. There has been steadily mounting interest in identifying 1) the rates at which dental materials corrode, 2) the mechanisms by which they corrode, 3) the variables which effect 1-2 above, and 4) if good predictive methods can be developed to correlate in vivo corrosion performance with a battery of test procedures and to then design new, improved alloys. The experiments to be carried out will attempt to answer some of these questions. First, in vivo experiments will be conducted in which the metals are placed in a removable palatal appliance and worn for 35 days by 30 human volunteers. In the clinical trial, the metals will be electrochemically tested using methods which do not alter the metal surface. The balance of the study will be done in vitro in artificial saliva electrolytes in which component compositions are systematically varied and the sample surfaces are carefully abraded. In both phases of the study, AC and DC electrochemical tests will be performed on five classes of dental casting alloys and will be related to the microscopic surface damage. The correspondence between in vivo and in vitro electrochemical test and microscopic examination results will be carefully investigated. At the conclusion of the project, 1) knowledge will have been obtained of the best means for testing and assessing corrosion of selected dental materials, 2) a safe and valid means for measurement of corrosion in the oral cavity will have been developed, and 3) criteria will have been developed on which to base the rational engineering design of new dental materials.